The differential diagnosis of purpura from a morphologic perspective.

Diseases associated with purpura range from the most common and trivial of human afflictions to some of the most devastating and rapidly fatal syndromes known. In order to sort the simple from the sinister, it is necessary to use not only the history and general physical examination, but also various morphologic components of the purpuric lesions themselves to suggest likely pathophysiologies of hemorrhage. Findings such as erythema, livedo reticularis, size of hemorrhage, presence or absence of palpability, symmetry or retiform patterning of lesions, and presence and extent of necrosis or eschar formation all can serve as clues to the likely etiologies of hemorrhage. Effective communication about purpuric syndromes requires information regarding the likely age of lesions described clinically or histologically and a precise description of the individual elements of the lesion. Such communication would be enhanced by eliminating the ambiguity inherent in the current usage of many of the terms employed to describe such lesions. This paper presents one possible approach to better use of the information that the morphology of purpuric lesions can provide.